Optical glass suffering little change in refractive index by radiation of light

ABSTRACT

An optical glass wherein an amount of change in refractive index (Δn: difference in refractive index between a state before radiation and a state after radiation) caused by radiation of laser beam at wavelength of 351 nm having average output power of 0.43W, pulse repetition rate of 5 kHz and pulse width of 400 ns for one hour is 5 ppm or below is provided. The optical glass comprises a fluorine ingredient and/or a titanium oxide ingredient and/or an arsenic oxide ingredient. The optical glass suffers little change in refractive index by radiation of strong light having wavelengths of 300 nm to 400 nm such as ultraviolet laser.

BACKGROUND OF THE INVENTION

[0001] This invention relates to an optical glass used in the nearultraviolet region and, more particularly, to an optical glass whichsuffers little change in refractive index by radiation of strong lighthaving wavelengths of 300 nm to 400 nm (e.g., super high pressuremercury vapor lamp and ultraviolet laser).

[0002] As an optical system using near ultraviolet rays, known in theart is an optical lithography for exposing and copying a fine pattern ofan integrated circuit on a wafer such as a silicon wafer, i.e., anexposure device called i-line stepper using the i-line (365 nm) of asuper high pressure mercury vapor lamp. In this exposure device, thereis an increasing tendency to expanding the exposure area with increasein integration in LSI. In an optical system of the i-line stepper,lenses having a diameter of 200 mm or over is generally used. Theoptical glass for i-line used for these lenses are required to have veryhigh homogeneity, to have internal transmittance for i-line of 99% orover in glass having thickness of 10 mm and to be free fromdeterioration due to ultraviolet radiation, i.e., solarization.

[0003] For this reason, the optical glasses for i-line are produced onthe basis of established technique including adoption of high puritymaterials including little impurities, use of cleaner steps for mixingand melting of materials and removal of strain by highly-homogeneousmelting and precision annealing.

[0004] However, as integration of LSI tends to increase further, it isdesired for the i-line stepper to have improved exposure and copyingcapabilities and durability over a long period of time and opticallenses used for the i-line stepper are desired to have high homogeneity,high transmittance, resistivity to solarization and also resistivity tothe i-line radiation, namely little change in refractive index by i-lineradiation.

[0005] As to change in refractive index by radiation of light, there isa phenomenon called the compaction phenomenon in which synthetic quartzglass undergoes changes in transmittance and density by radiation ofexcimer laser beam of a high level over a long period of time withresulting change in refractive index and the shape of glass surface.

[0006] The synthetic quartz glass is produced by synthesizing siliconoxide in the form of fine powder by burning silicon tetrachloride withoxyhydrogen flame and sintering this silicon oxide powder by heating itat a high temperature. That is, it is synthesized by the reaction:

SiCl₄+2O₂+4H₂→SiO₂+4HCl+2H₂O

[0007] The compaction phenomenon is considered to occur due to ions (OH⁻and H⁺) derived from water content remaining in the synthesized quartzglass and/or cutting of the Si—O bond caused by incompleteness ofreaction.

[0008] In the optical glasses for i-line offered for the i-lineradiation, occurrence of the compaction phenomenon has not beenspecifically known.

[0009] It has unexpectedly been found that, in the optical glass fori-line, deterioration in homogeneity due to change in refractive indexand increase in strain, and deformation in the shape of the glasssurface take place, in the same manner as was known in synthetic quartzglass, in a portion where ultraviolet ray or laser beam of a high levelwithin the wavelength range from 300 nm to 400 nm has been radiated and,therefore, the optical glass for i-line does not possess sufficientresistivity to light. An optical system using such optical glasses,therefore, tend to produce deterioration in image quality which willcause a problem in further increase in integration of LSI andimprovement in the exposure and copying capabilities of the i-linestepper.

[0010] For example, PBL1Y which is an optical glass for i-line made byOhara K. K. has undergone change in refractive index (Δn) ofΔn=+9.0×10⁻⁶ in a portion where laser beam having wavelength of 355 nmhas been radiated by a Q-switch pulse solid laser under conditions ofoutput of 1.2W, beam diameter of 2.6 mm, radiation time of 3 hours andtotal pulse number of 5.4×10⁷ pulses.

[0011] It is, therefore, an object of the present invention to providean optical glass having excellent resistivity to change by radiation oflight in which change in refractive index caused by radiation ofultraviolet ray or laser beam of a high level having wavelengths withina range from 300 nm to 400 nm is restrained.

SUMMARY OF THE INVENTION

[0012] Studies and experiments made by the inventors of the presentinvention for achieving the above described object of the invention haveresulted in the finding, which has led to the invention, that additionof fluorine ingredient and/or titanium oxide ingredient and/or arsenicoxide ingredient as a glass component unexpectedly has an effect ofrestraining change in refractive index by radiation of light. Morespecifically, a glass which suffers little change in refractive index byradiation of ultraviolet ray can be obtained by (1) in a Si₂—PbO-alkalimetal oxide glass, addition of a relatively small amount of fluorineingredient, and/or addition of As₂O₃ ingredient as a refining agentinstead of Sb₂O₃ ingredient, and/or addition of TiO₂ ingredient theamount of which is so small that influence to transmittance can beignored, (2) in a Si₂—B₂O₃-alkali metal oxide and/or an alkaline earthmetal oxide glass, addition of fluorine ingredient, and/or addition ofAs₂O₃ ingredient as a refining agent instead of Sb₂O₃ ingredient, and/oraddition of TiO₂ ingredient the amount of which is so small thatinfluence to transmittance can be ignored and (3) in aP₂O₅—Al₂O₃-alkaline earth fluoride glass, non-addition of a refiningagent and TiO₂ ingredient, or addition of a very small amount of atleast one of these ingredients.

[0013] For achieving the above described object of the invention, thereis provided an optical glass wherein an amount of change in refractiveindex (Δn: difference in refractive index between a state beforeradiation and a state after radiation) caused by radiation of laser beamat wavelength of 351 nm having average output power of 0.43W, pulserepetition rate of 5 kHz and pulse width of 400 ns for one hour is 5 ppmor below.

[0014] In one aspect of the invention, the optical glass comprises afluorine ingredient, and/or a titanium oxide ingredient, and/or anarsenic oxide ingredient.

[0015] In another aspect of the invention, the optical glass comprises,in mass %, a total amount of 0.1-45% of F in one or more fluorides asthe fluorine ingredient, and/or 0.001-0.5% of TiO₂ as the titanium oxideingredient, and/or 0.001-1% of As₂O₃ as the arsenic oxide ingredient.

[0016] In another aspect of the invention, the optical glass comprises,in mass %, SiO₂ 40-70% PbO 14-50% Na₂O and/or K₂O in the total amount of 8-17% where Na₂O  0-14% and K₂O  0-15% B₂O₃  0-5% As₂O₃  0-1% Sb₂O₃ 0-1% TiO₂  0-0.2% and fluoride or fluorides substituting for the aboveoxide or oxides partially or entirely, a total amount of F contained inthe fluoride or fluorides being 0-2%.

[0017] In another aspect of the invention, the optical glass comprises,in mass %, SiO₂ 30-70% B₂O₃  3-20% Al₂O₃  0-6% Li₂O  0-5% Na₂O + K₂O +BaO + ZnO in the total amount of 10-45% where Na₂O  0-13% K₂O  0-12% BaO 0-42% and ZnO  0-7% PbO  0-2% TiO₂  0-0.5% As₂O₃  0-1% Sb₂O₃  0-1% andfluoride or fluorides substituting for the above oxide or oxidespartially or entirely, a total amount of F contained in the fluoride orfluorides being 0-11%.

[0018] In another aspect of the invention, the above described SiO₂—PbOoptical glass comprises, in mass %, Li₂O 0-2% CaO 0-2% SrO 0-2% BaO 0-5%Al₂O₃ 0-2% the total amount of one or more of the Li₂O, CaO, SrO, BaOand Al₂O₃ ingredients being 5% or below.

[0019] In another aspect of the invention, the above described SiO₂—B₂O₃optical glass comprises, in mass %, CaO 0-2% SrO 0-2% ZrO₂ 0-2% thetotal amount of one or more of the CaO, SrO and ZrO₂ ingredients being2% or below.

[0020] In another aspect of the invention, the optical glass comprises,in mass %, P₂O₅ 4-39% Al₂O₃ 0-9% MgO 0-5% CaO 0-6% SrO 0-9% BaO 0-10%Y₂O₃ + La₂O₃ + Gd₂O₃ + Yb₂O₃ in the total amount of 0-20% Where Y₂O₃0-10% La₂O₃ 0-10% Gd₂O₃ 0-20% and Yb₂O₃ 0-10% TiO₂ 0-0.1% SnO₂ 0-1%As₂O₃ 0-0.5% Sb₂O₃ 0-0.5% AlF₃ 0-29% MgF₂ 0-8% CaF₂ 0-27% SrF₂ 0-27%BaF₂ 10-47% YF₃ 0-10% LaF₃ 0-10% GdF₃ 0-10% LiF 0-3% NaF 0-1% KF 0-1%the total amount of F in one or more of the fluorides being 10-45% andthe total amount of one or more of MgF₂, CaF₂, SrF₂ and BaF₂ being30-70%.

DETAILED DESCRIPTION OF THE INVENTION

[0021] First, reason for defining an amount of change in refractiveindex (Δn: difference in refractive index between a state beforeradiation and a state after radiation) caused by radiation of laser beamat wavelength of 351 nm having average output power of 0.43W, pulserepetition rate of 5 kHz and pulse width of 400 ns for one hour to be 5ppm or below will be described.

[0022] Studies and experiments conducted by the inventors of the presentinvention have revealed that a glass which satisfies the above describedcondition, when it is exposed to radiation of ultraviolet ray of a highoutput power or continuous laser beam in a wavelength region of 300nm-400 nm, does not cause deterioration in homogeneity, distortion ordeformation in the glass surface shape due to change in refractive indexbut maintains sufficient resistance to light for use as an optical glassfor I-line and, therefore, an optical system using this glass does notdeteriorate image quality but can increase integration of LSI andimprove the exposure and copying capabilities.

[0023] Reasons for limiting the composition ranges of the respectiveingredients in the optical glass of the invention as described abovewill now be described.

[0024] In the SiO₂—PbO-alkali metal oxide glass, the SiO²⁻ ingredient isan indispensable ingredient for forming glass and can impart the glasswith properties which are peculiar to the SiO₂—PbO glass by combinationwith the PbO ingredient. If the amount of this ingredient is less than40%, refractive index tends to become excessively high and transmittancebecomes insufficient in a short wavelength region which is unsuitablefor an optical system using i-line such as an i-line exposure device. Ifthe amount of this ingredient exceeds 70%, viscosity of the glassbecomes too high with resulting difficulty in providing a homogeneousglass.

[0025] The PbO ingredient is effective for producing a high-refractive,high dispersion glass and for properly dropping viscosity of the glass.If the amount of this ingredient is less than 14%, the glass becomeshard and it becomes difficult to provide a homogeneous glass. If theamount of this ingredient exceeds 50%, refractive index becomes too highand it becomes difficult to obtain sufficiently high transmittance in ashort wavelength region.

[0026] The Na₂O and K₂O ingredients are effective for accelerate meltingof the SiO₂ and PbO ingredients in glass materials and adjustingviscosity of the glass. If the amount of the Na₂O ingredient exceeds 14%or the amount of the K₂O ingredient exceeds 15%, it is undesirablebecause chemical properties of the glass such as weather-proof propertyand acid-proof property are deteriorated. If the total amount of theseingredients is less than 8%, the above described effects cannot beachieved sufficiently and, therefore, viscosity of the glass becomes toohigh to obtain a homogeneous glass. If the total amount of theseingredient exceeds 17%, the chemical properties of the glass such asweather-proof property and acid-proof property are deteriorated.

[0027] The B₂O₃ ingredient may be added as an optional ingredient. Thisingredient functions as a glass forming ingredient in the same manner asthe SiO₂ ingredient. If, however, this ingredient is added in a largeamount in the SiO₂—PbO-alkali metal glass, it tends to causedeterioration in the chemical properties and, therefore, the amount ofthis ingredient should preferably be 5% or less.

[0028] The As₂O₃ and Sb₂O₃ ingredients are effective as refining aidsfor the glass and, besides, the As₂O₃ ingredient is effective forrestraining the compaction phenomenon in the glass and, therefore, theseingredients may be added as optional ingredients. For attaining theseeffects, addition of each ingredient in an amount up to 1% will suffice.In a case where neither the fluorine ingredient nor the TiO₂ ingredientis present in the SiO₂—PbO-alkali metal oxide glass, the As₂O₃ingredient should be added in an amount of 0.001-1% in order to minimizethe change in refractive index due to the compaction phenomenon.

[0029] The TiO₂ ingredient is effective for adjusting refractive indexand Abbe number of the glass, and restraining the compaction phenomenonand solarization due to radiation of ultraviolet ray or laser beam of ahigh-level. If a large amount of this ingredient is added, transmittancein the short wavelength region is deteriorated and, therefore, theamount of this ingredient should preferably be 0.2% or less. In a casewhere neither the fluorine ingredient nor the As₂O₃ ingredient ispresent in the SiO₂—PbO-alkali metal glass, the TiO₂ ingredient shouldbe added in an amount of 0.001-0.2% in order to minimize the change inrefractive index due to the compaction phenomenon.

[0030] The fluorine ingredient may be added as an optional ingredient asfluoride or fluorides substituting for the above described oxide oroxides partially or entirely. This ingredient is effective forrestraining the compaction phenomenon of the glass due to radiation ofultraviolet ray or laser beam of a high level, and adjusting refractiveindex and viscosity of the glass. If the total amount of fluorinecontained in the fluoride or fluorides exceeds 2%, volatilization of thefluorine ingredient becomes excessive with resulting difficulty inproviding a homogeneous glass. In a case where neither the As₂O₃ingredient nor the TiO₂ ingredient is present in the SiO₂—PbO-alkalimetal oxide glass, the fluorine ingredient should be added in a totalamount of 0.1-2% in order to minimize the change in refractive index dueto the compaction phenomenon.

[0031] In the SiO₂—PbO-alkali metal oxide glass of the invention, theLi₂O, CaO, SrO and Al₂O₃ ingredients may be added as optionalingredients up to 2% respectively and the BaO ingredient may be added asan optional ingredient up to 5% in order to adjust viscosity, refractiveindex, chemical properties and stability of the glass. The total amountof one or more of the Li₂O, CaO, SrO, Al₂O₃ and BaO ingredients shouldbe 5% or below.

[0032] In the SiO₂—B₂O₃-alkali metal oxide and/or alkaline earth metaloxide glass, the SiO²⁻ingredient is an indispensable ingredient forforming of the glass in the same manner as in the case ofSiO²⁻—PbO-alkali metal oxide glass. If the amount of this ingredient isless than 30%, it is undesirable because a relatively large amount ofB₂O₃ and BaO ingredients is required and, moreover, refractive indexbecomes too high and the chemical properties are deteriorated. If theamount of this ingredient exceeds 70%, viscosity of the glass becomestoo high with resulting difficulty in providing a homogeneous glass.

[0033] The B₂O₃ ingredient is, like the SiO₂ ingredient, an oxide whichforms the glass and is effective for making a low dispersion glass andadjusting viscosity of the glass. If the amount of this ingredient isless than 3%, these effects cannot be achieved sufficiently. If theamount of this ingredient exceeds 20%, it is undesirable because thechemical properties are deteriorated. The Al₂O₃ ingredient is effectivefor improving chemical properties of the glass, and adjusting viscosityand refractive index of the glass. If the amount of this ingredientexceeds 6%, viscosity of the glass becomes too high.

[0034] The Li₂O ingredient is effective for accelerating melting ofglass materials, and it is less likely to causes decrease in refractiveindex and deterioration in chemical properties than in other alkalimetal oxides. If the amount of this ingredient exceeds 5%, it isundesirable because devitrification of the glass increases.

[0035] The Na₂O and K₂O ingredients are effective for acceleratingmelting of glass materials and a stable glass can be produced even incase these ingredients are added in a large amount. If, however, theamounts of the Na₂O ingredient and the K₂O ingredient exceed 13% and 12%respectively, it is undesirable because chemical properties aredeteriorated.

[0036] The BaO ingredient is effective for improving refractive indexwithout excessively increasing dispersion of the glass (i.e., withoutexcessively decreasing Abbe number) and providing a stable glass havinghigh resistivity to devitrification over a wide range of glasscomposition. If the amount of this ingredient exceeds 42%, chemicalproperties of the glass is extremely deteriorated.

[0037] The ZnO ingredient is effective for improving refractive index,adjusting viscosity and improving resistivity to devitrification. If theamount of this ingredient exceeds 7%, it is undesirable because decreasein transmittance in the short wavelength region tends to result.

[0038] For obtaining a glass which is stable, has excellent chemicalproperties and has excellent transmittance even in the short wavelengthregion, the total amount of one or more of the Na₂O ingredient, the K₂Oingredient, the BaO ingredient and the ZnO ingredient should preferablybe 10-45%.

[0039] The PbO ingredient and the TiO₂ ingredient are effective forpreventing solarization in the SiO₂—B₂O₃-alkali metal oxide and/oralkaline earth metal oxide glass. Further, the TiO₂ ingredient iseffective for restraining the compaction phenomenon. Addition ofexcessive amounts of these ingredients, however, causes deterioration intransmittance in the short wavelength region and, therefore, the amountsof these ingredients should preferably be up to 2% and 0.5%respectively. In a case where neither the fluorine ingredient nor theAs₂O₃ ingredient is present in the SiO₂—B₂O₃-alkali metal oxide and/oralkaline earth metal oxide glass, the TiO₂ ingredient should be added inan amount of 0.001-0.5% for minimizing the change in refractive indexcaused by the compaction phenomenon.

[0040] The As₂O₃ ingredient and the Sb₂O₃ ingredients are effective asrefining aids for the glass and, further, the As₂O₃ is effective forrestraining the compaction phenomenon of the glass and, therefore, theseingredients may be added as optional ingredients. For attaining theseeffects, however, it will suffice if these ingredients are added up to1% respectively. In a case where neither the fluorine ingredient nor theTiO₂ ingredient is present in the SiO₂—PbO-alkali metal oxide and/oralkaline earth metal oxide glass, the As₂O₃ ingredient should be addedin an amount of 0.001-1% for minimizing the change in refractive indexcaused by the compaction phenomenon.

[0041] The fluorine ingredient may be added as an optional ingredient asfluoride or fluorides substituting for the above described oxide oroxides partially or entirely. This ingredient is effective forrestraining the compaction phenomenon of the glass due to radiation ofultraviolet ray or laser beam of a high level, and adjusting refractiveindex and viscosity of the glass. If the total amount of fluorinecontained in the fluoride or fluorides exceeds 11%, the glass tends tobecome opaque, refractive index becomes too low and volatilization ofthe fluorine ingredient becomes excessive with resulting difficulty inobtaining a homogeneous glass. In a case where neither the As₂O³⁻ingredient nor the TiO₂ ingredient is present in the SiO₂—PbO-alkalimetal oxide glass, the fluorine ingredient should be added in a totalamount of 0.1-11% in order to minimize the change in refractive indexdue to the compaction phenomenon.

[0042] In addition to the above described ingredients, one or more ofthe CaO ingredient, SrO ingredient and ZrO₂ ingredient may be added in atotal amount of up to 2%.

[0043] In the P₂O₅—Al₂O₃-alkaline earth fluoride glass, the P₂O₅ingredient is a glass forming ingredient. If the amount of thisingredient is less than 4%, it is difficult to provide a stable glasshaving excellent resistivity to devitrification. If the amount of thisingredient exceeds 39%, the Abbe number becomes too small and the lowdispersion characteristic which is an advantageous feature of thecomposition of the invention becomes difficult to attain.

[0044] The Al₂O₃ ingredient is an ingredient which, by coexistence withthe P₂O₅ ingredient, forms the structure of the glass and also iseffective for improving chemical properties of the glass. If the amountof this ingredient exceeds 9%, devitrification increases.

[0045] The MgO, CaO, SrO and BaO ingredients included in the glass inthe form of phosphates are beneficial for improving stability andchemical properties of the glass and adjusting refractive index and Abbenumber. If the amounts of these ingredients exceed 5%, 6%, 9% and 10%respectively, it is undesirable because devitriifcation tends toincrease rather than decrease. For making a glass which is not likely tocause devitrification, a total amount of one or more of theseingredients should preferably be 20% or below.

[0046] The Y₂O₃, La₂O₃, Gd₂O₃ and Yb₂O₃ ingredients are effective forincreasing refractive index without decreasing the Abbe number,preventing occurrence of devitrification and improving chemicalproperties of the glass. If the amounts of these ingredients exceed 10%,10%, 20% and 10% respectively, it is undesirable because reistivity todevitrification is deteriorated. If the total amount of one or more ofthese ingredients exceed 20%, it is undesirable because resistivity todevitrification is deteriorated.

[0047] The TiO₂ ingredient is effective for improving refractive indexof the glass, preventing solalization and minimaizing the change inrefractive index due to the compaction phenomenon. For these reasons, itmay be added as required as an optional ingredient. It will suffice ifthis ingredient is added in an amount of 0.1% or below. Addition of thisingredient in excess of 0.1% is undesirable because it will causedeterioration in transmittance of the glass in the short wavelengthregion.

[0048] The SnO₂ ingredient is effective for improving refractive indexof the glass and preventing devitrification. It wll suffice if thisingredient is added in an amount of 1% or below.

[0049] The As₂O₃ ingredient and the Sb₂O₃ ingredients are effective asrefining aids for the glass and, further, the As₂O₃ is effective forrestraining the compaction phenomenon of the glass and, therefore, theseingredients may be added as optional ingredients. For attaining theseeffects, however, it will suffice if these ingredients are added up to0.5% respectively.

[0050] The AlF₃ ingredient is effective for decreasing dispersion of theglass and preventing devitrification. If the amount of this ingredientexceeds 29%, the stability of the glass is deteriorated and crystalstend to precipitate in the glass.

[0051] The MgF₂, CaF₂, SrF₂ and BaF₂ ingredients are effective forpreventing devitrification of the glass. If the amount of the BaF₂ingredient is less than 10%, it becomes difficult to obtain a chemicallystable glass. If the amounts of the MgF₂, CaF₂, SrF₂ and BaF₂ exceed 8%,27%, 27% and 47% respectively, devitrification increases rather thandecreases. A proper total amount of one or more of the MgF₂, CaF₂, SrF₂and BaF₂ ingredients is 30-70%.

[0052] The YF₃, LaF₃ and GdF₃ ingredients are effective for increasingrefractive index and improving resistivity to devitrification. Additionof each of these ingredients up to 10% will suffice.

[0053] The LiF, NaF and KF are effective for improving resistivity todevitrification. Addition of these ingredients in amounts exceeding 3%,1% and 1% respectively is not proper because it will increasedevitrification rather than decrease it.

[0054] In the P₂O₅—Al²⁻O₃-alkaline earth fluoride glass, it is properthat a total amount of F contained in the fluoride or fluorides shouldbe 10-45% in order to minimize the change in refractive index of theglass due to the compaction phenomenon. The above described oxides maybe substituted by fluorides and the above described fluorides may besubstituted by oxides within a range in which the ratio of metal ion,oxygen ion and fluorine ion of the respective oxides and fluorides ismaintained.

EXAMPLES

[0055] Examples of the optical glass made according to the inventionwill now be described. Examples No. 1 to No. 24 shown in Tables 1 to 4are examples of composition of the SiO₂—PbO-alkali metal oxide glass ofthe present invention. Examples No. 25 to No. 38 shown in Tables 5 and 6are examples of composition of the SiO₂—B₂O₃-alkali metal oxide and/oralkaline earth metal oxide glass of the present invention. Examples No.39 to 59 shown in Tables 7 to 9 are examples of composition of theP₂O₅—Al₂O₃-alkaline earth metal fluoride glass of the present invention.

[0056] Table 10 shows comparison (Comparison I and Comparison II)between Examples No. 60 to No. 64 of the SiO₂—PbO-alkali meal oxideglass of the present invention and Comparative Examples No. A and No. Bof the prior art glasses.

[0057] Table 11 shows comparison (Comparison III and Comparison IV)between Examples No. 65 and No. 66 of the SiO₂—B₂O₃-alkali metal oxideand/or alkaline earth metal oxide glass of the present invention andComparative Examples No. C and No. D of the prior art glasses.

[0058] In Tables 1 to 11, Δn (ppm) represents an amount of change inrefractive index between a state before radiation and a state afterradiation in a portion where radiation of laser beam having beamdiameter of 2.0 mm, wavelength of 351 nm, average output power of 0.43W,pulse repetition rate of 5 kHz and pulse width of 400 ns has beenradiated for 1 hour.

[0059] Table 12 shows Examples No. 67 to No. 70 of the SiO₂—PbO-alkalimetal oxide glass of the present invention and Examples No. 71 to No. 73of the SiO₂—B₂O₃-alkali metal oxide and/or alkaline earth metal oxideglass of the present invention. Table 13 shows change in refractiveindex Δn (ppm) between a state before radiation and a state afterradiation in a portion where radiation of the above-mentioned laser beam(having wavelength of 351 nm and beam diameter of 2.0 mm) has been madeon the glasses shown in Table 12 under conditions of output andradiation time which are different from those of Tables 1 to 11. TABLE 1(mass %) 1 2 3 4 5 6 7 SiO₂ 61.390 66.000 63.000 64.800 53.200 55.88050.200 PbO 24.800 19.890 20.200 18.500 34.600 30.200 38.200 Na₂O 9.0006.100 6.500 9.200 6.700 6.000 5.400 K₂O 4.000 7.700 7.900 6.700 5.2007.600 5.400 As₂O₃ 0.200 0.300 0.299 0.300 0.295 Sb₂O₃ 0.100 0.300 Al₂O₃0.400 K₂SiF₆ 1.900 0.500 KHF₂ 0.600 TiO₂ 0.010 0.010 0.001 0.020 0.005B₂O₃ 0.500 total 100.000 100.000 100.000 100.000 100.000 100.000 100.000F 0.292 0.983 0.259 nd 1.5481 1.5317 1.5317 1.5317 1.5814 1.5673 1.5955ν d 45.8 49.0 49.0 49.0 40.8 42.8 39.3 Δ n (ppm) 3.1 3.2 2.0 2.5 4.9 3.94.7

[0060] TABLE 2 (mass %) 8 9 10 11 12 13 14 SiO₂ 49.700 45.500 53.10053.100 53.100 51.995 40.000 PbO 38.200 44.900 34.700 32.700 29.70034.000 44.800 Na₂O 10.800 4.000 5.700 6.700 6.700 6.600 5.000 K₂O 4.8003.700 4.700 4.700 5.100 5.000 As₂O₃ 0.295 0.295 0.295 0.295 0.295 0.200Sb₂O₃ 0.300 K₂SiF₆ 0.500 0.500 0.500 2.000 KHF₂ 1.000 0.500 B₂O₃ 5.000TiO₂ 0.005 0.005 0.005 0.005 0.005 0.005 Li₂O 2.000 CaO 2.000 BaO 5.000Total 100.000 100.000 100.000 100.000 100.000 100.000 100.000 F 0.4860.243 0.259 0.259 0.259 1.035 nd 1.5955 1.6200 1.5866 1.5800 1.58011.5717 1.6258 ν d 38.7 36.3 40.9 40.8 40.9 41.7 36.9 Δ n(ppm) 4.5 4.24.6 4.8 3.9 4.6 4.5

[0061] TABLE 3 (mass %) 15 16 17 18 19 20 SiO₂ 68.95 41.00 63.00 66.0045.00 53.00 PbO 14.75 50.00 15.00 18.00 38.00 32.00 Na₂O 7.90 8.50 8.7014.00 6.70 K₂O 5.40 6.00 15.00 6.00 As₂O₃ 0.30 0.30 0.30 0.20 0.30 0.30Al₂O₃ 1.00 2.00 K₂SiF₆ 1.80 KHF₂ 1.20 0.20 B₂O₃ 0.50 5.00 1.70 SrO 2.00Total 100.00 100.00 100.00 100.00 100.00 100.00 F 0.58 0.10 0.93 nd1.5094 1.6407 1.5171 1.5271 1.5998 1.5785 ν d 55.5 34.7 54.0 50.3 38.841.4 Δ n(ppm) 2.3 4.5 3.3 2.5 4.6 4.6

[0062] TABLE 4 (mass %) 21 22 23 24 SiO₂ 58.80 59.74 52.64 51.65 PbO25.05 25.00 34.80 34.77 Na₂O 9.30 9.20 6.92 6.92 K₂O 4.80 4.70 4.34 5.35As₂O₃ 0.20 0.20 0.10 0.10 Al₂O₃ 0.30 0.20 0.20 0.20 K₂SiF₆ 1.54 0.951.00 1.00 TiO₂ 0.01 0.01 0.01 total 100.00 100.00 100.00 100.00 F 0.800.49 0.52 0.52 nd 1.5464 1.5470 1.5790 1.5781 ν d 45.8 45.8 40.9 41.0 Δn(ppm) 2.9 2.4 4.3 3.9

[0063] TABLE 5 (mass %) 25 26 27 28 29 30 31 SiO₂ 64.950 55.850 55.35042.000 35.550 30.000 68.990 B₂O₃ 14.900 13.050 6.050 13.600 16.00020.000 11.100 Al₂O₃ 2.300 0.500 0.600 4.200 4.500 5.500 Li₂O 3.000 2.0002.000 2.000 Na₂O 9.250 1.200 0.300 0.300 9.550 K₂O 6.850 11.450 8.7007.750 BaO 16.850 37.050 40.750 40.000 1.550 ZnO 5.750 1.000 PbO 1.0952.000 0.500 TiO₂ 0.005 0.050 0.100 0.010 As₂O₃ 0.150 0.250 0.400 0.4000.300 Sb₂O₃ 0.010 0.250 0.050 K₂SiF₆ 19.090 KHF₂ 0.500 0.350 0.200 CaO2.000 Total 100.000 100.000 100.000 100.000 100.000 100.000 100.000 F0.243 9.879 0.170 0.097 Nd 1.5163 1.4875 1.5567 1.5891 1.6031 1.60561.5163 N d 64.1 70.2 58.7 61.2 60.6 61.1 64.1 Δ n(ppm) 0.7 0.0 0.5 0.50.7 0.3 0.0

[0064] TABLE 6 (mass %) 32 33 34 35 36 37 38 SiO₂ 67.20 67.80 40.0034.55 49.00 55.80 35.50 B₂O₃ 3.60 4.10 12.30 18.00 17.90 13.05 16.00Al₂O₃ 4.50 5.50 0.30 0.50 4.50 Li₂O 2.00 2.00 Na₂O 12.50 12.10 0.30 0.300.50 K₂O 6.13 6.15 12.00 11.40 0.20 BaO 10.22 9.45 38.00 38.75 40.80 PbO0.50 TiO₂ 0.20 0.50 0.04 0.10 As₂O₃ 0.35 0.40 0.40 0.20 0.01 0.40 Sb₂O₃0.20 K₂SiF₆ 19.20 KHF₂ 20.60 SrO 2.00 ZrO₂ 2.00 Total 100.00 100.00100.00 100.00 100.00 100.00 100.00 F 10.02 9.94 Nd 1.5184 1.5184 1.59621.5989 1.4850 1.4860 1.6025 N d 60.3 60.3 60.5 60.3 70.1 69.7 60.5 Δn(ppm) 0.4 0.2 0.4 0.3 0.1 0.1 0.5

[0065] TABLE 7 (mass %) 39 40 41 42 43 44 45 46 P₂O₅ 27.45 22.45 21.055.55 10.85 9.35 19.40 4.85 Al₂O₃ 6.55 5.35 5.05 1.35 2.60 2.20 3.95 1.15AlF₃ 7.25 11.55 12.45 24.30 24.05 28.30 27.20 MgF₂ 4.45 6.05 5.10 5.204.25 5.30 4.05 CaF₂ 11.20 15.80 16.05 25.55 20.95 16.65 20.20 SrF₂ 18.0020.35 25.85 26.10 24.00 26.75 22.00 21.55 BaF₂ 25.10 18.45 14.45 11.8013.20 10.65 44.50 15.00 YF₃ 5.00 NaF 0.10 KF 0.15 1.00 Y₂O₃ 3.00 La₂O₃5.00 SnO₂ 0.05 SrO 0.80 2.10 Total 100.00 100.00 100.00 100.00 100.00100.00 100.00 100.00 F 23.97 29.37 30.32 42.60 39.28 40.94 16.30 42.94Nd 1.5296 1.5043 1.5006 1.4353 1.4505 1.4541 1.5632 1.4388 N d 76.2 79.481.1 85.5 81.6 90.5 69.8 95.1 Δ n(ppm) 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0

[0066] TABLE 8 (mass %) 47 48 49 50 51 52 53 54 P₂O₅ 25.00 38.20 22.6020.00 32.15 21.50 11.70 20.15 Al₂O₃ 6.00 8.60 5.40 1.80 3.30 2.80 2.55AlF₃ 10.00 7.50 26.50 13.75 MgF₂ 0.50 2.35 8.00 4.00 4.90 CaF₂ 9.0010.00 7.00 15.00 14.00 15.40 SrF₂ 15.00 14.00 20.00 9.20 13.00 23.0015.85 BaF₂ 28.00 22.00 47.00 20.00 25.00 22.00 12.00 15.80 YF₃ 3.00 LaF₃5.00 2.00 GdF₃ 10.00 2.60 LiF 2.50 Y₂O₃ 10.00 5.50 6.00 La₂O₃ 10.00 6.20Gd₂O₃ 5.00 20.00 5.00 SnO₂ 1.00 MgO 5.00 2.20 CaO 6.00 SrO 9.00 BaO 2.4010.00 As₂O₃ 0.10 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00100.00 F 12.06 16.83 17.14 22.04 22.21 23.54 36.80 28.73 Nd 1.58261.5913 1.5583 1.5783 1.5532 1.5022 1.4565 1.4973 N d 70.3 72.6 70.6 72.071.2 79.2 90.1 80.9 Δ n(ppm) 0.1 0.0 0.0 0.1 0.1 0.1 0.1 0.2

[0067] TABLE 9 (mass %) 55 56 57 58 59 P₂O₅ 4.00 25.00 25.00 11.70 24.00Al₂O₃ 1.00 7.00 6.00 2.80 6.00 AlF₃ 27.00 25.50 MgF₂ 5.00 4.50 2.00 CaF₂21.00 5.00 13.50 2.00 SrF₂ 21.00 15.00 15.00 22.50 13.00 BaF₂ 16.0019.00 23.00 12.50 27.00 YF₃ 5.00 10.00 LaF₃ 5.00 10.00 5.00 NaF 1.00Y₂O₃ 10.00 5.00 La₂O₃ 10.00 5.00 Gd₂O₃ 5.00 Yb₂O₃ 10.00 CaO 6.00 SrO1.00 BaO 9.00 1.00 Total 100.00 100.00 100.00 100.00 100.00 F 37.5229.12 14.87 36.59 13.13 Nd 1.4378 1.5816 1.5822 1.4562 1.5820 N d 97.170.2 69.9 90.0 70.1 Δ n(ppm) 0.1 0.1 0.2 0.1 0.1

[0068] TABLE 10 (mass %) Comparison I Comparison II 60 61 Com. Ex. A 6263 64 Com. Ex. B SiO₂ 63.00 65.30 66.00 53.10 53.05 52.00 53.10 PbO20.20 18.50 19.90 34.70 34.70 34.00 34.70 Na₂O 6.50 9.20 6.10 6.70 6.706.60 6.70 K₂O 7.90 6.70 7.70 5.20 5.20 5.10 5.20 As₂O₃ 0.30 0.30 0.30Sb₂O₃ 0.10 0.30 0.30 0.30 Al₂O₃ 0.40 K₂SiF₆ 1.90 2.00 TiO₂ 0.05 total100.00 100.00 100.00 100.00 100.00 100.00 100.00 F 0.98 1.04 Nd 1.53171.5317 1.5317 1.5786 1.5801 1.5717 1.5800 ν d 49.0 49.0 49.0 41.0 40.941.7 40.8 Δ n(ppm) 2.9 3.4 6.3 4.9 4.5 4.2 10.0

[0069] TABLE 11 Comparison III Comparison IV 65 Com. Ex. C 66 Com. Ex. DSiO₂ 67.80 67.20 68.99 64.95 B₂O₃ 4.10 3.60 11.10 14.90 Al₂O₃ 2.30 Na₂O12.10 12.50 9.55 9.25 K₂O 6.15 6.13 7.75 6.85 BaO 9.45 10.22 1.55 ZnO1.00 PbO 1.60 TiO₂ 0.20 0.01 Sb₂O₃ 0.20 0.35 0.05 0.15 Total 100.00100.00 100.00 100.00 Nd 1.5184 1.5184 1.5163 1.5163 ν d 60.3 60.3 64.164.1 Δ n(ppm) 0.2 6.0 0.0 7.0

[0070] TABLE 12 (mass %) No. 67 68 69 70 71 72 73 SiO₂ 63.20 65.48 51.6251.62 57.85 68.50 69.34 B₂O₃ 13.52 3.99 11.11 PbO 20.33 20.27 34.8034.80 K₂O 7.96 7.79 5.35 5.35 11.85 6.00 7.76 Na₂O 6.51 6.18 6.93 6.9211.85 9.55 Al₂O 0.37 0.20 0.20 0.50 K₂SiF₆ 1.53 1.00 1.00 16.23 As₂O₃0.28 0.10 0.10 0.01 0.20 0.03 Sb₂O₃ 0.10 TiO₂ 0.01 0.04 0.20 0.01 BaO9.26 1.19 ZnO 1.01 total 100.00 100.00 100.00 100.00 100.00 100.00100.00 F 0.79 0.52 0.52 8.40 nd 1.53168 1.53145 1.57904 1.57807 1.487131.51820 1.51593 ν d 48.9 49.0 40.9 41.0 70.2 60.3 64.1

[0071] TABLE 13 No. Average (mass %) Output Δ n (ppm) Power(W) Time 6768 69 70 71 72 73 0.10 165 hrs 0.2 0.60 10 min. 0.3 0.60 15 min. 0.30.60 30 min. 0.5 0.60 1 hour 0.5 0.60 10 min. 0.6 0.60 1 hour 1.1 2.0010 min. 0.7 1.20 15 min. 1.0 2.00 25 min. 1.6 2.00 10 min. 0.5 1.20 15min. 0.8 2.00 25 min. 1.3 1.50 3 hrs 0.0 2.65 3 hrs. 0.5 2.65 3 hrs. 0.6

[0072] As shown in Tables 1 to 12, the amount of change Δn in a periodbetween before and after radiation of laser beam in the glasses ofExamples No. 1 to No. 73 is 5 ppm or below. The glasses of Examples No.60 to No. 66 shown in Tables 10 and 11 all have a smaller amount ofchange (Δn) in a period between before and after radiation of laser beamthan the prior art glasses of Comparative Examples No. A to No. D whichhave similar contents of SiO₂, PbO, B₂O₃, alkali metal oxide and BaO aswell as similar values of nd and νd to these Examples of the inventionand, thus, show the advantageous effects of containing the fluorineingredient and/or the titanium oxide ingredeint and/or the arsenic oxideingredient.

[0073] The glasses of the above described examples of the invention canbe easily manufactured by weighing and mixing optical glass materialssuch as oxides, carbonates, nitrates, hydroxides, phosphates andfluorides, melting the materials at 900-1500° C. for about 3 hours to 10hours in a platinum container and/or a quartz container and thereafterrefining, stirring, and homogenizing the melt and cooling the melt to apredetermined temperature, and casting it in a preheated mold andannealing it.

[0074] In summing up, the optical glass of the present invention is anoptical glass wherein an amount of change in refractive index (Δn:difference in refractive index between a state before radiation and astate after radiation) caused by radiation of laser beam at wavelengthof 351 nm having average output power of 0.43W, pulse repetition rate of5 kHz and pulse width of 400 ns for one hour is 5 ppm or below.

[0075] It is also an optical glass comprising a fluorine ingredientand/or a titanium oxide ingredient and/or an arsenic oxide ingredient.It is also a SiO₂—PbO-alkali metal oxide glass containing a fluorineingredient and/or a titanium oxide ingredient and/or an arsenic oxideingredient respectively of a specific composition range, or aSiO₂—B₂O₃-alkali metal oxide and/or alkaline earth metal oxide glasscontaining a fluorine ingredient and/or a titanium oxide ingredientand/or an arsenic oxide ingredient respectively of a specificcomposition range, or a P₂O₅—Al₂O₃-alkaline earth metal fluoride glasscontaining a fluorine ingredient and/or a titanium oxide ingredientand/or an arsenic oxide ingredient respectively of a specificcomposition range. In the optical glasses of the present invention, anamount of change (Δn) in refractive index in a portion where ultravioletray or laser beam of a wavelength in the range from 300 nm to 400 nmhaving a high level has been radiated is very small. Accordingly, byusing the optical glass of the present invention in a high-precisionoptical system using light of a high energy density such as high levelultraviolet ray and laser beam in the wavelength reion of 300 nm to 400nm, deterioration in homogeneity of the glass, increase in distortion inthe image or deformation in the surface shape of the glass hardly takesplace and, therefore distortion or bleeding in the image hardly takesplace. For these reasons, the optical glass of the invention is veryuseful. By using, for example, the optical glass of the invention forlenses of an optical system or lighting system of an i-line stepper,exposure and copying of a highly integrated LSI pattern can be made witha high resolution.

What is claimed is:
 1. An optical glass wherein an amount of change inrefractive index (Δn: difference in refractive index between a statebefore radiation and a state after radiation) caused by radiation oflaser beam at wavelength of 351 nm having average output power of 0.43W,pulse repetition rate of 5 kHz and pulse width of 400 ns for one hour is5 ppm or below.
 2. An optical glass as defined in claim 1 comprising afluorine ingredient and/or a titanium oxide ingredient and/or an arsenicoxide ingredient.
 3. An optical glass as defined in claim 2 comprising,in mass %, a total amount of 0.1-45% of F in one or more fluorides asthe fluorine ingredient and/or 0.001-0.5% of TiO₂ as the titanium oxideingredient and/or 0.001-1% of As₂O₃ as the arsenic oxide ingredient. 4.An optical glass as defined in claim 3 comprising, in mass %, SiO₂40-70% PbO 14-50% Na₂O and/or K₂O in the total amount of  8-17% whereNa₂O  0-14% and K₂O  0-15% B₂O₃  0-5% As₂O₃  0-1% Sb₂O₃  0-1% TiO₂ 0-0.2% and fluoride or fluorides substituting for the above oxide oroxides partially or entirely, a total amount of F contained in thefluoride or fluorides being 0-2%.


5. An optical glass as defined in claim 3 comprising, in mass %, SiO₂30-70% B₂O₃  3-20% Al₂O₃  0-6% Li₂O  0-5% Na₂O + K₂O + BaO + ZnO in thetotal amount of 10-45% where Na₂O  0-13% K₂O  0-12% BaO  0-42% and ZnO 0-7% PbO  0-2% TiO₂  0-0.5% As₂O₃  0-1% Sb₂O₃  0-1% and fluoride orfluorides substituting for the above oxide or oxides partially orentirely, a total amount of F contained in the fluoride or fluoridesbeing 0-11%.


6. An optical glass as defined in claim 4 comprising, in mass %, Li₂O0-2% CaO 0-2% SrO 0-2% BaO 0-5% Al₂O₃ 0-2% the total amount of one ormore of the Li₂O, CaO, SrO, BaO and Al₂O₃ ingredients being 5% or below.


7. An optical glass as defined in claim 5 comprising, in mass %, CaO0-2% SrO 0-2% ZrO₂ 0-2%


8. An optical glass as defined in claim 3 comprising, mass %, P₂O₅ 4-39% Al₂O₃  0-9% MgO  0-5% CaO  0-6% SrO  0-9% BaO  0-10% Y₂O₃ +La₂O₃ + Gd₂O₃ + Yb₂O₃  0-20% in the total amount of Where Y₂O₃  0-10%La₂O₃  0-10% Gd₂O₃  0-20% and Yb₂O₃  0-10% TiO₂  0-0.1% SnO₂  0-1% As₂O₃ 0-0.5% Sb₂O₃  0-0.5% AlF₃  0-29% MgF₂  0-8% CaF₂  0-27% SrF₂  0-27%BaF₂ 10-47% YF₃  0-10% LaF₃  0-10% GdF₃  0-10% LiF  0-3% NaF  0-1% DF 0-1%